A variety of systems and applications use stacks of sheets or plates, which may be made of metal, paper, plastic and the like. Printing plates (hereinafter singly or collectively referred to as “plates”) are typically stacked in a tray or similar container, which houses the plates and facilitates their protection, transportation and handling.
A specific system using plates generally uses trays having specific dimensions. Trays can usually be set to contain plates of various sizes, but all plates in the same tray are of one size. Usually the plates are manually removed from the cassette or the shipping container and inserted into the trays for use by the system, for example, a plate imaging system.
Plates are usually packed in the cassette with intermediate paper sheets, hereinafter referred to as ‘separation paper’. The separation papers are disposed during loading into the imaging device by a mechanism such as described in U.S. Pat. No. 6,164,637 assigned to the common assignee of the present invention.
A typical conventional plate feeding system from a tray is shown schematically in FIG. 1. Plates 12 are supplied, within a tray 14, stacked one on top of the other with separation papers 16 between the plates.
Various mechanisms have been developed for removing a single plate 12 from the tray 14 and loading it using loading arm 18 to the loading plane 23 of the imaging system 20. Usually the feeding system includes a mechanism for disposing of the separation paper 16 into a paper bin 22 illustrated, for example.
One such system is described in U.S. Pat. No. 5,785,309 assigned to the common assignee of the present invention. The loading method described has the disadvantage in that, if a different plate size needs to be loaded for a subsequent operation, then the tray in use needs to be replaced by a tray containing the required plate size, or the tray itself needs to be replenished with plates of the required size. Replacing trays is a costly procedure and time consuming operation.
U.S. Pat. No. 5,367,360 to McIlwraith et al. describes a method for loading plates from a single tray. In this case, the cardboard shipping container is used as a tray and the plates are lifted and loaded vertically by a vacuum system.
The use of several trays with the same system is known in the art of copiers, for example, where paper is loaded selectively from different trays. The trays are stacked one on top of the other, each having a separate loading mechanism.
U.S. Pat. Nos. 5,655,452, 5,738,014 5,791,250, 5,788,455 describe an apparatus and method of loading plates from a plurality of trays into an imaging device. The trays are stacked one on top of the other and moved by an elevator mechanism to allow a loading arm to enter between the trays and pick-up a specific plate.
U.S. Pat. No. 4,984,260 to Koyama describes an automatic loader for films used in radiation diagnostics. This loader employs static staggered cassettes, a belt-type picking mechanism, which moves the films to an irradiation station, which is placed on top of the cassettes.
Trays containing printing plates are heavy and bulky, and moving such tray up and down requires complicated and expensive mechanism and is time consuming. There is, thus a widely recognized need for an automatic and efficient handling system of loading plates of various sizes to a plate imaging system, without the need to move trays.
Furthermore, the loading device may contain a large space for disposing the separation papers, a flat table for pre-exposure operations, such as punching registration holes in the plates, and a picking arm. It is desired that those units be packed into minimum floor space.